Table of Contents
Regular Original Research Article
| Available Energy and Exergy | |
| Richard A. Gaggioli | 1-8 | An "available energy" is defined for every state of any system. The definition is independent of (a) the concept of work. (b) any reference environment, and (c) the makeup of the system (e.g. "macro" or "micro). On the basis of this available energy, given any composite system, the contribution of each subsystem to the available energy -- that is, the exergy content of a subsystem -- is defined, as well as the instantaneous "dead state" of the composite and each subsystem. Some pedagogical, scientific and engineering implications are discussed. |
| Maxwell's and Boltzmann's Triumphant Contributions to and Misconceived Interpretations of Thermodynamics | |
| Elias P. Gyftopoulos | 9-19 | The statistical interpretation is discussed and found to be inadequate to explain thermodynamic phenomena. Two alternative approaches to the statistical interpretation are summarized, one purely thermodynamic, and the other quantum-theoretic and thermodynamic. |
| Presentation of an Innovative Zero-Emission Cycle for Mitigating the Global Climate Change | |
| Philippe Mathieu | 21-30 | In the spectrum of possible options to cope with the global climate change, a novel technology based on the zero CO2 emission MATIANT cycle (contraction of the names of the 2 designers : MATHIEU and IANTOVSKI) is presented here. This latter is basically a regenerative gas cycle operating on CO2 as the working fluid and using O2 as the fuel oxidiser in the combustion chambers. The cycle uses the highest temperatures and pressures compatible with the most advanced materials in the steam and gas turbines. In addition, reheat and staged compression with intercooling are used. Therefore the optimized cycle efficiency rises up to around 45% when operating on natural gas. A big asset of the system is its ability to remove totally the CO2 produced in the combustion process in liquid or supercritical state and at high pressure, making it ready for transportation, for reuse or for final storage. It avoids the cost in performance (decrease of efficiency and power output) and in money of the CO2 capture by a MEA scrubber. The assets and drawbacks of the cycle are mentioned. The technical issues for the design of a prototype plant are examined. |
| An Analytical Procedure for the Assessment of Malfunctions in Thermomechanical Systems | |
| Javier Royo, Antonio Valero, Alejandro Zaleta-Aguilar | 31-43 | The behaviour of the thermal components is commonly described through a set of internal parameters: isentropic efficiencies, pressure ratios, effectiveness factors, pressure losses, temperature relations or differences, et cetera. In this paper a new type of internal parameters, the internal parameters θ (Royo 1994, Royo and Valero 1995) are defined, that are specially adequate for the characterisation of thermal systems in an analytical way. When a component of a thermal plant displays an internal deterioration (intrinsic malfunction) its performance gets worse. This fact is reflected in a variation of the internal parameters describing its behaviour. On the other hand, the remaining components of the plant may be affected (induced malfunction) because they are working under different operating conditions from the usual ones. Knowledge of variations of the internal parameters in each component of a thermal plant does not suffice to determine their performance state under these new conditions. Additional information is needed. The dissipation temperature parameter can supply it (Royo 1994, Royo et al. 1997) as is explained in this paper. Internal θ parameters and the dissipation temperature parameters are appropriate tools for the study analysis and evaluation of malfunctions in thermomechanical systems. Three examples of this are shown, trying to quantify the influence of an intrinsic malfunction on the whole plant. This paper shows a strickingly new and simple vision of the analysis of thermal systems. |
| Non-Equilibrium and Classical Thermodynamics for Practical Systems: Today Closer Together Than Ever Before | |
| Stanislaw Sieniutycz | 45-59 | We deal with applications of thermodynamics and availability theory to practical systems where a certain external control is possible in order to achieve improved performance. In particular, results of optimization of endoreversible processes which yield mechanical work are discussed. Equations of dynamics which follow from energy balance and transfer equations are difference constraints for optimizing work. Irreversibilities caused by the energy transport are essential. A model system is developed which incorporates finite heat resistances for an energy conversion process, and may be extended to take into account friction, heat leakage, mixing and other effects decreasing the thermodynamic efficiency. Deviation of efficiencies from their limiting Carnot values are analyzed in terms of the finite heat flux. The variational calculus and optimal control theories are shown to be the basic tools when formulating and solving problems with maximizing work. For a finite-time passage of a resource body between two given temperatures, optimality of an irreversible process manifests itself as a connection between the process duration and an optimal intensity. Extremal performance functions which describe extremal work are found in terms of final states and process duration measured in terms of the number of the heat transfer units. An extended exergy that has an irreversible component and simplifies to the classical thermal exergy in the limit of infinite duration is discussed. With this exergy performance criteria and bounds are defined for real processes occurring in a finite time. Enhanced bounds for the work released from an engine system or added to a heat-pump system are evaluated. A comparison between the optimization in thermodynamics (with exergy) and in economics (with costs) is made. Examples of exergy analysis to seek the best adjustable parameters of solar collectors, separation processes (distillation) and a chemical process with catalyst deactivation are discussed. |
ISSN: 2146-1511